Currently, the graphical installer is exceptionally slow, and a big part of
the reason is that mtrr wasn't enabled in the -boot kernel. Now that it is
(see bug 47296), anaconda should take advantage of it.
(IIRC, XFree86 3.x doesn't do this automatically for fbdev devices. I
could be wrong.)

This is not an X problem. XFree86 uses MTRR if it is available. If
it is not available then it is not built into the kernel. I am reassigning
to the kernel component, however IMHO it is just unneeded code bloat in
the boot kernel. I'll leave that decision up to the kernel team though.